I was reacquainted with Titanium Nitride care of a woodworker on YouTube the other day. It’s being used to protect tool surfaces from wear. Is that a coincidence or is there something special about nitrogen as a dopant?
> Like carbides, nitrides are often refractory materials owing to their high lattice energy, which reflects the strong bonding of "N3−" to with metal cation(s). Thus, cubic boron nitride, titanium nitride, and silicon nitride are used as cutting materials and hard coatings. Hexagonal boron nitride, which adopts a layered structure, is a useful high-temperature lubricant akin to molybdenum disulfide.
Beyond that, when it comes to cutting tools in particular, there's often interesting solid phase and surface chemistry with layered gradients of oxynitrides forming at depth from the working interface that have similar properties to the base nitride and absorb energy through multiple phase changes and chemical dissociations before ultimate mass reduction, extending the life of the working surface
Less hard, to be more precise [1]. “Strong” and “weak” are way imprecise terms in engineering.
The simplest example is whether it’s strong under pressure (a brick is, a rope isn’t) or under tension (a rope is, a brick isn’t), but there are tons of other properties that are an indicator of strength of a material (https://en.wikipedia.org/wiki/Strength_of_materials), and this may beat diamond in some of them.
[1] reading Wikipedia, even that isn’t simple: “There are three main types of hardness measurements: scratch, indentation, and rebound. Within each of these classes of measurement there are individual measurement scales. For practical reasons conversion tables are used to convert between one scale and another.”
> Like carbides, nitrides are often refractory materials owing to their high lattice energy, which reflects the strong bonding of "N3−" to with metal cation(s). Thus, cubic boron nitride, titanium nitride, and silicon nitride are used as cutting materials and hard coatings. Hexagonal boron nitride, which adopts a layered structure, is a useful high-temperature lubricant akin to molybdenum disulfide.
Beyond that, when it comes to cutting tools in particular, there's often interesting solid phase and surface chemistry with layered gradients of oxynitrides forming at depth from the working interface that have similar properties to the base nitride and absorb energy through multiple phase changes and chemical dissociations before ultimate mass reduction, extending the life of the working surface